Researchers are warning the planet is facing a growing risk of abrupt and irreversible climatic shifts unless carbon emissions are reduced.

A new report says greenhouse gas emissions and other indicators are closing in on the upper limits forecast by the United Nation’s Intergovernmental Panel on Climate Change two years ago.

The University of Copenhagen released the Synthesis Report overnight which draws on 1,600 scientific contributions to a global climate summit held in Copenhagen earlier this year.

Australian National University Professor Will Steffen was one of 12 researchers who contributed to the report, along with Sir Nicholas Stern.

"The climate system is now moving out of the envelope of variability in which our civilisations have developed," Professor Steffen said.

"In some aspects it’s moving right near the upper range of earlier projections, this gives us a sense of urgency.

"A good example of that is sea level rise which is moving right to the upper level of projections we’ve had around now for about 20 years. It’s a pretty fundamental parameter because it is related partly at least to how fast the oceans are warming. That’s where about 90 per cent of the extra heat is going.

"So we have a very good indicator now that the climate … system is shifting pretty definitely and pretty rapidly."

Professor Steffen says time is running out to implement meaningful cuts in emissions.

"If we want to keep temperatures below two degrees – which is an often quoted guardrail – we pretty much need to see our emissions peak within the next six to 10 years and then drop very quickly after that," he said.

Tipping points

Professor Steffen says some systems like the Great Barrier Reef are reaching their tipping points.

"Basically a tipping point means that a system is not going to respond in a nice smooth way to increased CO2 in the atmosphere or increased temperature," he said.

"You can see temperature rise, temperature rise, and nothing happening to a system. An example being the Indian monsoon. And then with the small additional increase in temperature, it may flip to a much drier state.

"So basically a tipping element means you can push and push and push a system – a bit like a canoe. If you are starting to tip over in a canoe, it always comes back until you just reach that critical point and then you tip over.

"Natural systems do this. [An example] is the Great Barrier Reef – a big natural ecosystem which is resilient to a point but once you pass that point, then it will change very quickly."

Sense of urgency

Professor Steffen says the report lends a sense of urgency to the upcoming climate negotiations in Copenhagen.

"I think I could paraphrase the Prime Minister of Denmark … who looked at this and said ‘alright, this is giving me a sense of urgency. This is giving me a sense that we have to come out of Copenhagen in December with a widely agreed road map that includes the big developing countries like China and India as well as the major players in the industrialised world like the United States’," he said.

"We have to get to that level of remit, we can’t wait for another round of negotiations.

"So his bottom line message was – he took the science on board and said ‘now is the time we have got to move’."